Recently, in radio networks for mobile phones, PHSs (Personal Handy-phone Systems), and the like, the occurrence of coverage holes has become a problem. A coverage hole is an area in which communication is unavailable and its range dynamically changes depending on the surrounding radio environment. It is difficult for mobile terminal devices to perform communication in a coverage hole; therefore, it is important in terms of the connectivity of radio networks to minimize the occurrence of coverage holes.
Therefore, there has recently been a technology for detecting coverage holes. One form of the technology for detecting coverage holes is such that radio quality, location information, and the like obtained when a radio link failure occurs are recorded in a mobile terminal device when triggered by the radio link failure (RLF: Radio Link Failure) that occurs when a communicating mobile terminal device passes through a coverage hole. When the mobile terminal device recovers from the radio link failure, the mobile terminal device that has recorded the radio quality, location information, and the like obtained when the radio link failure occurs notifies a control server of the recorded information. Based on the information whose notification is made by each mobile terminal device, the control server instructs each base station to, for example, adjust the transmission power value of a base station that becomes a factor in causing a coverage hole or to turn on the power.
Patent Literature 1: Japanese Laid-open Patent Publication No. 2002-271833
Meanwhile, with the widespread use of mobile terminal devices, data communication traffic due to the Internet connection has been increasing, and in response to this, the total power consumption of networks due to the Internet connection has also been increasing. In view of such an increase in the total power consumption, for example, in the 3GPP (3rd Generation Partnership Project) 32.826, specifications have been examined in which the total power consumption is reduced by introducing network operations that are in accordance with the traffic.
For example, in the specifications of the 3GPP, a base station collects information on the traffic, the electric energy, and the like and notifies a control server of the collected information. The control server determines the electric energy in accordance with the traffic based on the information whose notification is made by a plurality of base stations and, for example, indicates a setting transmission power value to each base station or instructs each base station to turn on/off the power. Consequently, in the specifications of the 3GPP, the total power consumption of the networks due to the Internet connection is reduced.
In the specifications of the 3GPP, although the total power consumption can be reduced, a coverage hole may occur around a base station for which the transmission power value is adjusted or that has its power off. In other words, in the specifications of the 3GPP, in order to reduce the total power consumption, the transmission power value of a base station is adjusted or the power of a base station is turned off without examining a coverage hole in advance during the design phase of the network; therefore, a coverage hole may occur.
However, in the conventionally technology, because a coverage hole is detected when triggered by a radio link failure, there is a problem in that it is difficult for a coverage hole that occurs when a base station performs power control to be efficiently detected.